Distillation of liquid solutions expanded along a curvilinear surface

ABSTRACT

Method for distillation of a liquid, particularly sea water, in which the liquid flows thru a plurality of stages each of which includes at least one cell through which the liquid flows and in which steam produced by evaporation is separated from the unevaporated liquid in order to obtain a condensate. The method employs one or more expansion nozzles in each cell through which the liquid expands and is thus converted partly into its vapour phase as a result of the reduction in pressure. The composite liquid and gaseous fluid passes along a curved flow surface which, as a result of the centrifugal forces created effects separation of the liquid from the steam. The steam is then condensed and the remaining liquid is sent to a diffusor in which its speed is transformed into pressure, delivering thus a pressure greater than the one at the inlet of the expansion nozzle. The liquid passes then through a heat exchanger and may then either be re-cycled through the cell or passed to a warmer or cooler cell.

United States Patent Bidard Sept. 3, 1974 DISTILLATIDN OF LIQUID SOLUTIONS EXPANDED ALONG A CURVILINEAR SURFACE [75] Inventor: Rene Bidard, Paris, France [73] Assignee: Compagnie Electro-Mecanique, Paris, France 22 Filed: Sept. 4, 1973 21 Appl. No.: 393,817

Related US. Application Data [60] Continuation of Ser. No. 133,115, April 12, 1971, abandoned, which is a division of Ser. No. 802,106, Feb. 25, 1969, Pat. NO. 3,619,379.

[30] Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 2,510,233 6/1950 Kermer 159/17 2,510,548 6/1950 Brunjes 159/17 3,003,931 10/1961 Worthen et a1 203/88 X 3,251,397 5/1966 Lens 159/17 HE AT EXCHANGER 8 4 9 SUPPLY 1 I PIPE EXPANSION 1 NOZZLE 3,299,649 1/1967 McGrath et a1. 203/10 X 3,427,227 2/1969 Chamberlin 203/11 X 3,536,591 10/1970 Lotz 202/174 Primary ExaminerNorman Yudkoff Assistant ExaminerDavid Edwards Attorney, Agent, or Firm Pierce, Scheffler, & Parker [57] ABSTRACT Method for distillation of a liquid, particularly sea water, in which the liquid flows thru a plurality of stages each of which includes at least one cell through which the liquid flows and in which steam produced by evaporation is separated from the unevaporated liquid in order to obtain a condensate. The method employs one or more expansion nozzles in each cell through which the liquid expands and is thus converted partly into its vapour phase as a result of the reduction in pressure. The composite liquid and gaseous fluid 'passes along a curved flow surface which, as a result of the centrifugal forces created effects separation of the liquid from the steam. The steam is then conidensed and the remaining liquid is sent to a diffusor in which its speed is transformed into pressure, delivering thus a pressure greater than the one at the inlet of the expansion nozzle. The liquid passes then through a heat exchanger and may then either be re-cycled through the cell or passed to a warmer or cooler cell.

6 Claims, 9 Drawing Figures VAPOR. FLOW TO COOLER /CELL' 5 PAIENIEDSEP 3.833.480

SHE! 1 If 4 I SER LIouIo BRANCH CONDEN PIPE SUPPLY PIPE HEAT EXCHANGER VA PO'R FLOW TO COLLER CELL D E V R U 4 1 .E. R M; FU RF UF D 3 SUPPLY 1 I PIPE EXPANSION 1 NOZZLE Fig.2

PATENTEDSEP 31974 3.833.480

SVHEEI 30? 4 Fig.4

DISTILLATION OF LIQUID SOLUTIONS EXPANDED ALONG A CURVILINEAR SURFACE This is a continuation of application Ser. No. 133,1 15 filed Apr. 12, 1971, now abandoned, which is a division of application Ser. No. 802,106, filed Feb. 25, 1969, now US. Pat. No. 3,619,379.

The invention concerns a method for the distillation of a liquid, especially sea-water, in several stages each of which have at least one cell through which the liquid flows and in which steam produced by evaporation is separated from the unevaporated liquid in order to obtain a condensate.

Conventional methods of this kind require a considerable amount of mechanical or electrical power and a correspondingly large plant in order to ensure that the liquid circulates in the tubes of the heat exchangers and/or from one distillation stage to the next.

An object of the invention is to avoid these disadvantages by achieving the circulation through all the elements by thermodynamic means. This problem is solved by a method employing a combination of the following elements which are known individually andof which there is at least one in each cell, the liquid to be distilled flowing through these elements in series:

- an expansion nozzle in which steam occurs due to a reduction in pressure so that the flow velocity of the liquid increases;

- a curved surface along which the liquid flows and whereby due to the influence of centrifugal forces an inwardly directed free surface forms where the steam separates from the liquid;

- a diffusor which in the main takes only a part of the unevaporated liquid and converts part of its velocity into pressure which at the outlet of the diffusor is higher than at the inlet of the expansion nozzle; and a heat exchanger through which at least a part of the unevaporated liquid flows, whereby it is heated.

The expansion nozzle, of which there may be several in each cell and which are thenarranged in parallel, is so constructed that the liquid can expand when it flows through it, whereby during the expansion or pressure reduction it partly evaporates. An emulsion forms which when it is discharged from the nozzle has a velocity considerably higher than that which the liquid alone would have for the same expansion without any evaporation.

The liquid flows with a high velocity along the curved flow surface which for instance can be cylindrical. Due to the influence of the centrifugal forces a separation occurs between the remaining liquid and the steam, whereby the liquid moves outwards and a free surface is formed towards the inside of the curve where the steam is discharged along the flow path. The steam is passed to a condenser through which a cooler medium flows. This medium can either be unevaporated liquid from a colder cell or a medium which comes from an external cold source. The condensate which collects in the condenser is extracted and is one of the two products of this cell. The other one, the unevaporated liquid which has become somewhat concentrated due to evaporation, passes on to the succeding constructional element, as described below.

In the diffusor, several of which can be arranged in each cell, the high velocity of the unevaporated liquid is retarded, whereby a part of its flow energy is converted into pressure. In accordance with the invention the diffusor is so constructed that the pressure of the liquid at its outlet is appreciably higher than at the inlet of the expansion nozzle.

At least part of the liquid which is discharged from the diffuser flows to the heat exchanger where it is heated. The liquid can thus either flow back to the inlet of the expansion nozzle, so that it is again expanded in the same cell and partly evaporated and then subjected to the subsequent process steps, or it can be passed to a warmer cell. When the liquid flows through the heat exchanger its pressure drops, but nevertheless the pressure is still high afterwards and as already mentioned is slightly above that at the inlet of the expansion nozzle.

Generally only part of the unevaporated liquid is recirculated through the same cell, because otherwise the concentration in this cell would rise to an indefinite degree, and a certain supplementary amount of liquid is always necessary in order to replace at least the evaporated liquid. The remaining part of the unevaporated liquid serves as a supplementary amount in one of the subsequent cells, which can be either a warmer or colder cell.

In the former case it is an advantage if the tapped-off liquid is heated before it is introduced into the next cell, this being achieved in a further heat exchanger. Normally the pressure inside the warmer cell is higher than that in the cell from which the liquid has been tapped. lt is, however, possible to introduce this suplementary amount of liquid into the warmer cell due to the fact that the pressure of the unevaporated liquid rises considerably when it passes through the diffusor so that it not only covers the pressure losses in the heat exchanger but can also overcome the pressure difference between the internal chambers of the two connected cells. In this case the introduction of the supplementary amount of liquid is generally not accompanied by an expansion and a considerable evaporation. It is also possible without departing from the spirit of the invention, to pass the entire amount of unevaporated liquid through this second heat exchanger and then to a warmer cell, although it is thermodynamically more favourable when only part of the liquid is tapped off and the remaining part is allowed to recirculate in the cell. I

It is to be noted that both the aforementioned heat exchangers in which a liquid is heated, are supplied with the necessary amount of heat either by the condensation of steam from another warmer cell or by means of heat from an external source.

If the tapped-off liquid is supplied to a colder cell as supplementary liquid, then also the pressure in this cell is lower. Without prior heating it is thus possible for expansion and partial evaporation to occur, whereby this can already take place in the supply pipe when it is suitably designed for this purpose.

The double possibility of introducing the tapped-off liquid into the next cell, either by raising or lowering the temperature and without having to provide a number of mechanical pumps, gives the designer considerable latitude. The steps of the process which has been described can be performed with various types of cells, some examples of which are illustrated in the accompanying drawings and also described.

FIG. 1 shows a semi-cylindrical form in a vertical section along the generatrix;

FIG. 2 is a modified form of that shown inFIG. 1;

FIG. 3a shows another constructional form; FIGS. 3b to 32 show details of FIG. 3a; FIGS. 4 and illustrate other constructional forms.

In all the Figures those parts which serve the same purpose are provided with the same reference num bers.

In FIG. 1 both the aforementioned possibilities the liquid tapped off in a cell and passed into a warmer or colder cell to act as supplementary liquid whereby actually one possibility excludes the other, are both shown in FIG. 1 for the sake of simplicity. Reference number 1 indicates the expansion nozzle, 2 the curved flow surface, 3 is the'difi'usor, and 4 the heat exchanger in which the liquid that flows back into the cell and is thus circulated afresh is heated 5 is the condenser in which the steam generated in the cell in question is condensed; in this case it is the same heat exchanger 4 of a colder cell. The flow path there is indicated by the arrow 6; in reality suitably arranged pipes form the flow path. The condensed liquid discharges through the pipe 7.

The free surface where the steam, which occurs due to the pressure reductions in the expansion nozzle, separates out is indicated by the broken line and corresponds to the curved surface 2. The separating surface between the emulsion region and the separated liquid is indicated by the dotted line.

When part of the unevaporated liquid is tapped off and supplied to a warmer cell as supplementary liquid, a heatexchanger 8 is provided for heating this liquid. The liquid which flows through the. heat exchangeris conveyed from the collector 9 through a pipe 10 to the next cell. As already "explained, the evaporated and tapped-off quantity has to be augmented again by way of the supply pipe 11.

Conditions are different when the tapped-off partial quantity has to be supplied to a colder 'cell'as supplementary liquid. Since no heating is necessary, elements 8, 9, 10 and 1 1. are not required and the partial quantity is tapped off after the diffusor 3 through the branch pipe 12 and supplied to the next cell. The necessary supplementary liquid'is supplied through the connection pipe 13 where,-when it has a suitable form, a first expansion and evaporation already occurs before the supplementary liquid reaches the expansion nozzle 1.

From the description of FIG. 1, it is obvious that for the first operating case (tapped-off liquid introduced into a warmer cell) elements 12 and 13 are not present.

For the two constructional examples which are combined in FIG. '1, the cells'can be arranged either side by side or one above the other. The length of the cells perpendicular to the plane of the drawing is optional. Moreover, since the supplementary quantity which is passed from one cellto the next constantly diminishes due to evaporation, it is possible to arrange two or more cells per stage in parallel at the beginning of each series of cells or the size of the cells can decrease in size as the quantity of supplementary liquid diminishes.

FIG. 2 shows a cell similar to that of FIG. 1, but the system for separating the steam from the unevaporated liquid is shown in more detail. The first separation occurs before the pressure is increased by the diffusor 3, namely along the curved flow surface 2 which is semicircular. The separation of the remaining steam bubbles as well as a slight further evaporation of the liquid occurs in a whirl chamber that is nearly closed along its periphery and which has a curved surface 14 which augments the curved flow surface 2.

When the cell is very long in the direction perpendicular to the plane of the drawing, it is necessary to subdivide the whirl chamber by means of walls parallel to the plane of the drawing, so that the passage of the steam between these walls in the direction of the arrow 6 is facilitated.

According to FIG. 3a the separation of the steam from the unevaporated liquid is achieved by means of a number of small whirl chambers 33 located in each cell, the entire amount of liquid of the cell flowing through these chambers in parallel.

FIG. 3b shows to a larger scale a whirl chamber in vertical section. FIG. 3c is a sectional view taken along the line a a in FIG. 3b at the level of the expansion nozzle 1, whilst FIG. 3d is a sectional view taken along the line /3-Bin FIG. 3b at the level of the diffusor 3. Such a whirlchamber can be made from a single metal sheet of the shape shown in FIG. 32 and which is bent to the required form. The free surface indicated by the broken lines in FIG. 3b occurs automatically in each whirl chamber due to the rotation of the liquid.

FIG. 3a shows an arrangement where a number of such whirl chambers 33 are located in one cell. A common pipe 15 supplies all the expansion nozzles of the whirl chambers and the unevaporated liquid discharged from the diffusors 3 of the whirl chambers passes to a common collecting chamber 16. The separated steam collects in an upper chamber 17 before it passes to the condenser 5.

Also in connection with this constructional example the reintroduction of the liquid discharged from the heat exchanger 4, as well as the possibility of passing on a certain amount of liquid and introducing a corresponding supplementary amount of liquid are shown. This constructional example, however, also provides a special construction for the case where the liquid. which is tapped off at 10 passes to a warmer cell, namely a pipe 11 for supplying the supplementary quantity which extends into the whirl chamber. When the partial amount of liquid which flows out through the branch which are separated by a wall 18 from the whirl chambers that are supplied by way of pipe 15.

FIG. 4 illustrates a constructional'example of the invention where each cell is provided with a large whirl chamber and the cells are arranged one above the other. This arrangement also comprises the following basic elements which have already been referred to.

a. The expansion nozzle, where during expansion a partial evaporation occurs. In the present example there are a number of expansion nozzles corresponding to the number of supply pipes, these being formed by annular blade grids, 1, 1 with intermediate channels between the blades which act as expansion nozzles. The ring 1, 1 completely surrounds the whirl chamber and can supply it along its entire periphery.

b. The curved flow surface, formed by a cylinder 2,

FIG. 2, a further evaporation also occurs here in the whirl chamber.

c. The diffusor where at its outlet the pressure of the unevaporated liquid is higher than that at the inlet of the expansion nozzle. In this constructional example there are several diffusors as is also the case with the expansion nozzles. These diffusors are in the form of annular blade grids, 3, 3' which are so shaped that in the intermediate channels the tangential components of the velocity are at least partly converted into pressure.

(I. The heat exchanger in which the liquid that has to be evaporated is heated.

Each half of FIG. 4 shows a different constructional form of the invention. The right hand side shows how a cell has to be constructed when the tapped-01f liquid flows to a warmer cell and serves as a supplementary quantity. In this case a heat exchanger 8 is provided which serves to heat the tapped-off liquid and also a collecting chamber 9 from which the liquid is discharged through pipe 10 to the warmer cell. The necessary supplementary liquid is supplied to the cell through pipe 11.

The left hand side of FIG. 4 illustrates the case where the tapped-off liquid flows to a colder cell and serves as a supplementary quantity, branch pipe 12 and connecting pipe 13 being provided for this purpose. Pipe 13 supplies a special part 19 of the annular grid 1, whereby the blades of this grid can be adapted to the outlets of part 19. v

It is to be noted that in FIG. 4 the upper cell is warmer and the lower one colder. A reverse arrangement is also possible and furthermore the cells can also be arranged next to each other.

The possibility of being able to allow the supplementary quantities of the cells to flow onward in a simple manner, either when the temperature rises or falls, enables a distillation unit to be provided having two series of cells which mutually complete each other. In one series, the supplementary quantities flow from cell to cell with increasing temperatures and in the other series with decreasing temperatures. The condensers of both series can be connected together in such a manner that' the heat calories for the supplementary quantity in the series having a rising temperature are supplied by the heat of a condensation from steam taken from the second series having a supplementary quantity with a falling temperature. This is possible when the thermal equilibrium is maintained.

FIG. 5 shows the arrangement for such a double series of cells, the first series with rising temperatures for the supplementary amounts being on the right side and the second series with falling temperaturs being on the left side. The cells of the first series are indicated by 1 2, n q,, the cells of the second series by 1 2 n :1 The supplementary quantities flow upwards in the first series and downwards in the second series.

For this method of operation it is necessary that the heat exchanger 8, which is provided for heating the supplementary quantity in the first series of cells, is surrounded by a condensation part of the second series and not by a condensation part of the first series. In the heat exchanger 8, a condensation of the steam also occurs which results from the reevaporation of the distilled liquid that is obtained from the cells which are located above the heat exchanger.

At the top of both series where the temperatures are highest, two heat exchangers 20 and 21 are provided which receive heat from a suitable source, for instance steam from a boiler. These heat exchangers heat on the one hand the liquid which recirculates in cells 1, and 1 and on the other hand the supplementary quantity which flows from cell 1, to 1 I Condensers 23 and 24 at the end of the unit where the temperatures are lowest serve both series as coolers, through which a cooling medium flows which enters at 25 and leaves at 26. A condenser 27 can also be provided for warming the supplementary quantity which passes at 28 into the lowest cell of the first series. The highly concentrated liquid which remains after the distillation, is discharged at 29 from the last cell of the second series.

Reference number 30 indicates the outlet for the liquid obtained from distillation. The liquid comes from the condensers of both series but its flow path through the whole unit is not shown. It is sufficient to note that it is collected in each stage in the corresponding cell of the second series whence it flows downwards from stage to stage in cascades; Due to successive expansion, part of the liquid evaporates, condenses again at the heat exchanger 8, and thus heats up the supplementary quantity of the first series. The details of this process are only indicated in cells q, and q by the arrows 31 and 32.

With such an arrangement the power necessary for circulating the liquid that has to be distilled is obtained in the whole system purely by thermodynamic means. The concentration of the liquid finally obtained can be regulated as desired by varying the proportion of the inner recirculation in all the cells. Moreover, the concentration of the liquid to be distilled which flows through pipe 22 from the first to the second series can be regulated by varying the amount of internal recirculation in one series with respect to that in other series, whereby any desired value between that at the inlet and that at the outlet can be obtained.

The method according to the invention has the following advantages due to the fact that only thermodynamic means are used for the transportation of all the media: less mechanical energy is required; less space is required because various auxiliary machinery is no longer necessary; the free circulation of the media results in a more efficient and simpler assembly of the distillation stages.

I claim:

1. A method for the distillation of an impure liquid which includes a plurality of stages operating at different temperatures and pressures, each stage operating according to a thermodynamic cycle which comprises the steps of heating an impure liquid, passing the heated liquid through an expansion zone at one end of the inside of a curvilinear surface for expansion of at least a portion of the heated liquid to obtain a mixture of impure liquid and vapor while converting the pres sure of the liquid to velocity, centrifugally passing the liquid having increased velocity around the inside of the curvilinear surface while separating the vapors from the unevaporated liquid, condensing the separated vapors to obtain a pure liquid, passing the unevaporated liquid through a diffusor zone at the other end of the inside of the curvilinear surface to reduce its velocity while increasing its pressure to a value higher than the pressure of the liquid before expansion, re-

heating at least a portion of the unevaporated liquid and repeating the cycle of steps.

2. A method as claimed in claim 1 wherein the at least a portion of the unevaporated liquid, the pressure of which has already been increased, is reheated by the heat obtained by the condensation of the vapor from a warmer stage, said reheated liquid being returned cyclically to the same stage for re-evaporation.

3. A method as claimed in claim 1 wherein a part of the unevaporated impure liquid after having been pressurized and reheated is supplied to a warmer stage and mixing the reheated part of the unevaporated impure liquid with the impure liquid circulating in the warmer stage.

4. A method as claimed in claim 1 wherein a part of the unevaporated impure liquid is supplied to a colder stage and mixed with the flow of the impure liquid circulating in the colder stage.

5. A method as claimed in claim 1 wherein the plurality of stages is divided into a first and a second series of successive stages, passing at least a part of the unevaporated impure liquid and in the first series of stages from each stage to a warmer stage in the series, withdrawing at least a part of the unevaporated liquid from the last stage of said first series at the highest temperature and highest pressure of the first series, further heating the withdrawn liquid and introducing it to the second series of stages, passing the withdrawn reheated liquid through successively colder stages of the second series, removing the unevaporated liquid from the last stage of the second series at the lowest temperature and lowest pressure of the second series and discarding said removed liquid.

6. A method as claimed in claim 1 wherein the second series of stages operate as multiflash distillation stages, and further comprising introducing to the stages of the second series only a portion of the unevaporated impure liquid from a preceeding stage.

- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 mm Dated Sent. lq'm Inventor ($7 Rene :B id ard It is certified that error appears in the above-identified patent and that said Letters Patent are hereby. corrected as shown below:

Claim 6, line v1 delete "1 and insert:

-5' Signed and s aled this 19th day of November 1974.

(SEAL) Attest:

C. MARSHALL DANN MCCOY M. GIBSON JRQ Commissioner of Patents Attesting Officerfl 

2. A method as claimed in claim 1 wherein the at least a portion of the unevaporated liquid, the pressure of which has already been increased, is reheated by the heat obtained by the condensation of the vapor from a warmer stage, said reheated liquid being returned cyclically to the same stage for re-evaporation.
 3. A method as claimed in claim 1 wherein a part of the unevaporated impure liquid after having been pressurized and reheated is supplied to a warmer stage and mixing the reheated part of the unevaporated impure liquid with the impure liquid circulating in the warmer stage.
 4. A method as claimed in claim 1 wherein a part of the unevaporated impure liquid is supplied to a colder stage and mixed with the flow of the impure liquid circulating in the colder stage.
 5. A method as claimed in claim 1 wherein the plurality of stages is divided into a first and a second series of successive stages, passing at least a part of the unevaporated impure liquid and in the first series of stages from each stage to a warmer stage in the series, withdrawing at least a part of the unevaporated liquid from the last stage of said first series at the highest temperature and highest pressure of the first series, further heating the withdrawn liquid and introducing it to the second series of stages, passing the withdrawn reheated liquid through successively colder stages of the second series, removing the unevaporated liquid from the last stage of the second series at the Lowest temperature and lowest pressure of the second series and discarding said removed liquid.
 6. A method as claimed in claim 1 wherein the second series of stages operate as multiflash distillation stages, and further comprising introducing to the stages of the second series only a portion of the unevaporated impure liquid from a preceeding stage. 